Timing Advance Validation

2. The terminal device of claim 1, wherein the indication of the distance between the terminal device and the other entity is based on a measure of a signal strength of signalling received from the other entity.

3. The terminal device of claim 1, wherein the indication of the change in distance between the terminal device and the other entity is based on a measure of a change in a signal strength of signalling received from the other entity.

4. The terminal device of claim 1, wherein the terminal device is further configured to determine the current timing advance should not be updated if the indication of the distance between the terminal device and the other entity is within a predetermined range.

5. The terminal device of claim 1, wherein the terminal device is further configured to determine the indication of the distance between the terminal device and the other entity using different position sensing technologies for different distances between the terminal device and the other entity.

6. The terminal device of claim 1, wherein the terminal device is further configured to determine an indication of a position for the other entity and to determine an indication of a position for the terminal device and to use these to determine the indication of the distance between the terminal device and the other entity.

7. The terminal device of claim 1, wherein the indication of the distance between the terminal device and the other entity comprises the current timing advance.

8. The terminal device of claim 1, wherein the timing advance validity threshold is determined from the indication of the distance between the terminal device and the other entity by taking account of a radio path loss model.

9. The terminal device of claim 8 wherein the radio path loss model is a free space radio path loss model or a Hata radio path loss model.

10. The terminal device of claim 1, wherein the timing advance validity threshold comprises an indication of a change in a signal strength of signalling received from the other entity.

11. The terminal device of claim 1, wherein to determine the timing advance validity threshold based on the indication of the distance between the terminal device and the other entity. the terminal device is further configured to compare the indication of the distance between the terminal device and the other entity with a plurality of ranges of values for the indication of the distance between the terminal device and the other entity, and select the timing advance validity threshold value according to which of the plurality of ranges of values for the indication of the distance between the terminal device and the other entity contains the determined indication of the distance between the terminal device and the other entity.

12. The terminal device of claim 11, wherein the terminal device is further configured to receive from the other entity an indication of a relationship between the plurality of ranges of values for the indication of the distance between the terminal device and the other entity and the corresponding timing advance validity threshold values.

13. The terminal device of claim 1, wherein the terminal device is further configured to use at least one further criterion to determine whether or not the timing advance value should be updated if the indication of distance between the terminal device and the other entity is within a predetermined range.

14. The terminal device of claim 13, wherein the at least one additional criterion comprises the outcome of a comparison between a timing advance validity threshold and an indication of a change in a distance between the terminal device and a further entity in the wireless telecommimication system.

15. The terminal device of claim 1, wherein the terminal device is further configured to determine two timing advance validity thresholds based on the indication of the distance between the terminal device and the other entity, and to select one of the two timing advance validity thresholds to use for the comparison between the indication of the change in the distance between the terminal device and the other entity and the timing advance validity threshold based on whether the indication of a change in the distance between the terminal device and the other entity indicates the terminal device has moved towards or away from the other entity.

18. A non-transitory computer-readable medium encoded with computer-readable instructions that, when executed by circuitry of a terminal device, cause the circuitry of the terminal device to perfoiiu a method according to claim 16.

19. A non-transitory computer-readable medium encoded with computer-readable instructions that, when executed by circuitry of a terminal device, cause the circuitry of the terminal device to perform a method according to claim 17.